Process for recovering cyclopentene and conjugated c5-diolefins

ABSTRACT

CONJUGATED C5-DIOLEFINS AND CYCLOPENTENE ARE RECOVERED FROM A MIXTURE OF C5-HYDROCARBONS CONTAINING UNSATURATED C4-HYDROCARBONS BY A PROCESS WHICH INCLUDES THE FOLLOWING STEPS: (A) SUBJECTING SAID MIXTURE TO LIQUID-LIQUID EXTRACTION: (B) REMOVING PARAFFINS AND MONO-OLEFINS AS THERAFFINATE ( OF THE LIQUID-LIQUID EXTRACTION; (C) FEEDING THE EXTRACT SOLUTION TO AN EXTRACT REFLUX COLUMN; (D) SUBJECTING THE HEAD PRODUCT FROM THE EXTRACT REFLUX COLUMN TO DISTILLATION AND REMOVING C4-HYDROCARBONS AS THE HEAD FRACTION AND RETURNING THE SUMP PRODUCT TO THE LIQUID-LIQUID EXTRACTION STEP: AND (E) FEEDING THE SUMP PRODUCT FROM THE EXTRACT REFLUX COLUMN TO A DEGASSER WHEREIN C5-DIOLEFINIC HYDROCARBONS AND/OR CYCLOPENTENE ARE REMOVED AS THE HEAD PRODUCT AND THE SUMP PRODUCT IS RETURNED TO THE LIQUIDLIQUID EXTRACTION STEP.

y 1974 B. SCHLEPPIN GHOFF ET 1 PROCESS FOR RECOVERING CYCLOPENTENE AND CONJUGATED C 'DIOLEFINS Filed July 12, 1972 degasser Q,

extract reflux column distillation column extractor 3,810,831 PROCESS FOR RECOVERING CYCLOPENTENE AND CONJUGATED C -DIOLEFINS Bernhard Schleppinghotf and Helmut Scherb, Dormagen, and Hans Puxbaumer, Cologne, Germany, assignors to Erdolchemie Gesellschaft mit beschraukter Haftung, Cologne, Germany Filed July 12, 1972, Ser. No. 271,323 Claims priority, application Germany luly 21, 1971, P 21 36 495.4 Int. Cl. C07c 7/10; Cg 21/20 US. Cl. 208-321 4 Claims ABSTRACT OF THE DISCLOSURE Conjugated C -diolefins and cyclopentene are recovered from a mixture of C -hydrocarbons containing unsaturated C -hydrocarbons by a process which includes the following steps:

(a) subjecting said mixture to liquid-liquid extraction;

(b) removing paraflins and mono-olefins as therafiinate of the liquid-liquid extraction;

(c)feeding the extract solution to an extract reflux column;

(d) subjecting the head product from the extract reflux column to distillation and removing C.,-hydrocarbons as the head fraction and returning the sump product to the liquid-liquid extraction step; and

(e) feeding the sump product from the extract reflux column to a degasser wherein C diolefinic hydrocarbons and/or cyclopentene are removed as the head product and the sump product is returned to the liquid liquid extraction step.

BACKGROUND This invention relates to a process for recovering aliphatic c hydrocarbons having 2 conjugated double bonds and cyclopentene from a C -hydrocarbon fraction containing C -hydrocarbons.

A naphtha fraction known as cracked naphtha is formed during the thermal cracking of mineral oils or fractions thereof, containing inter alia paraffinic, olefinic and diolefinic hydrocarbons, more particularly isoprene, cyclopentadiene, cisand trans-1,3-pentadiene and cyclopentene. Further processing of this cracked naphtha by distillation yields a C -fraction, i.e. a hydrocarbon fraction containing mostly hydrocarbons having 5 carbon atoms. This C -hydrocarbon fraction consists of a mixture of paraffinic, olefinic and diolefinic hydrocarbons. However, C -fractions such as these contain a relatively large proportion of C -hydrocarbons, depending upon the level of separation achieved during pre-distillation of the cracked naphtha. These C -hydrocarbons are generally the more highly unsaturated compounds such as 1,2-butadiene, 1,3-butadiene and Z-butyne, in addition to the mono-unsaturated compounds cisand trans-Z-butene.

If a C -fraction of this kind containing C -hydrocarbons is extracted by a process of the kind described for example in The Oil and Gas Journal, vol. 65 (1967), 2, pp. 98-104, emulsion formation soon occurs in the lower chambers of the extractor, resulting in a continuous decrease in the throughput capacity in regard to the C hydrocarbons. Accordingly, the process cannot be worked continuously over prolonged periods.

SUMMARY The process of the invention for separating conjugated C -diolefins and cyclopentene from a mixture of paraflinic, olefinic and diolefinic C -hydrocarbons containing un- "United States Patent 0 saturated C.,-hydrocarbons includes the following steps (a) subjecting said mixture to liquid-liquid extraction; (b) removing paraflins and mono-olefins as the raffinate of the liquid-liquid extraction; (c) feeding the extract solution to an extract reflux column; (d) subjecting the head product from the extract reflux column to distillation and removing C -hydrocarbons as the head fraction and returning the sump product to the liquid-liquid extraction step; and (e) feeding the sump product from the extract reflux column to a degasser wherein C -diolefinic hydrocarbons and/or cyclopentene are removed as the head product and the sump product is returned to the liquid-liquid extraction step.

DESCRIPTION OF THE DRAWING The present invention will be more fully understood from the following description taken in conjunction with the accompanying drawing which is a schematic flow diagram illustrating a preferred embodiment for carrying out the process of the invention.

DESCRIPTION We have now found that aliphatic C -hydrocarbons having two conjugated double bonds and/or cyclopentene can be recovered from a mixture of paraflinic, olefinic and diolefinic C -hydrocarbons but which also contains unsaturated C hydrocarbons, providing the mixture to be treated is subjected to a liquid-liquid extraction with selective solvents, and the resulting extract solution is delivered to an extract reflux column in which:

(a) The 'C -hydrocarbons are completely degassed and enter the extract reflux which, before it is fed into the extractor, is distilled to separate. 01f 1,2-butadiene, 1,3- butadiene and Z-butyne; and

(b) The aliphatic C -hydrocarbons having two double bonds and/or cyclopentene from the sump of the extract reflux column are delivered to a degasser where these products are separated off from the extractant, which is then recycled to the extractor.

The process according to the invention can be carried out in an extraction installation of any kind. For example, the liquid-liquid extraction can be carried out in pulsed sieve-plate columns, in centrifugal extractors or in a mixer-settler battery.

Selective solvents suitable for use in the process according to the invention include solvents which are capable of extracting aliphatic C -hydrocarbons having two conjugated double bonds and cyclopentene whilst leaving monoolefins and paraflins as rafiinate. Specific examples of such suitable solvents include dialkyl sulphoxides such as dimethyl sulphoxide and diethyl sulphoxide, also furfurol, nitromethane, acetonitrile, dimethyl formamide, dimethyl acetate and butyrolactone.

It is preferred to use standard N-methylpyrrolidone which can be employed either as such or in the form of a mixture with water, having a water content of from 4 to 20% by weight. A mixture of N-methylpyrrolidone and water having a water content of from 6 to 12% by weight is particularly preferred.

The quantity in which the selective solvent is used should be at least sufficient to dissolve all the constituents to be extracted. In some cases, it is possible to use a considerable excess in relation to this minimum quantity, especially in cases where increased demands are imposed upon the diolefin content of the raflinate. Suitable ratios by volume of solvent to the starting material are in the range from 3:1 to 5:1.

The extraction temperature can be within a wide range, provided that, under the pressure and temperature conditions applied, it is lower than that temperature at which bubble formation occurs in the mixture, and provided that it is above the solidification temperature of the selective solvent. In most cases, especially Where N-methylpyrrolidone or N-methylpyrrolidone-water mixtures are used, temperatures of from 15 to 45 C. are applied. A slight excess pressure is generally maintained in the extraction column and in this case, the optimum working temperature is substantially 30 C.

In the practical application of the process according to the invention, it is preferred to maintain working conditions under which the ratio by weight of the throughput of extractant to the throughput of the starting material in the extraction zone is in the range of from 3 to 10 and most preferably in the range of to 8. The ratio by weight of the throughput of the extract reflux to the throughput of starting material is preferably in the range of from 0.6 to 1.4 and most preferably in the range of 0.8 to 1.2.

The process according to the invention is a continuously workable and economically advantageous extraction process by means of which aliphatic C -hydrocarbons having two conjugated double bonds and/or cyclopentene can be obtained in high yields and in highly pure form from hydrocarbon mixtures which, in addition to C -hydrocarbons, also contain C -hydrocarbons. This process is free from the disadvantages which accompany conventional techniques, such as the continuous reduction in throughput capacity and emulsion formation in the extractor.

Another advantage of the process according to the invention is that, by virtue of the intermediate separation column, the lower-boiling components which cause difliculties as separation continues can be separated otf from the extract reflux at this intermediate point in an economically advantageous manner. More particularly, in addition to separation of the C -hydrocarbons, 1,4-pentadiene for example, is simultaneously separated at this intermediate point. During production of the C -fraction, separation of 1,4-pentadiene by distillation is incomplete, even with intensive separation, and is accompanied by considerable losses of isoprene. Where liquid-liquid extraction is carried out by a conventional process, the 1,4- pentadiene accumulates in the extractor like the C -hydrocarbons which results in the aforementioned disadvantages.

The fraction rich in C -hydrocarbons which is separated ofl from the extract reflux by the process according to the invention can either be delivered together with crude cracked petrol to a hydrogenation stage so as to improve the quality of the standard petrol, or alternatively it can be directly delivered as a starting material for the recovery of 1,3-butadiene to an extractive distillation stage, for example, further improving the economy of the process according to the invention.

The process according to the invention can, of course be applied in conjunction with conventional working-up techniques. For example, in order to remove cyclopentadiene present in the starting material, the cyclopentadiene can be dimerized in conventional manner into dicyclopentadiene by thermal pretreatment of the starting material. Where liquid-liquid extraction is carried out with the aforementioned selective solvents, dicyclopentadiene enters the rafiinate together with the monoolefins and the paraflins (cf. DOS No. 1,941,704).

The proportion of solvent which, in the process according to the invention, is removed with the raflinate from the solvent circuit between the extractor, the extract recycle column and the degasser can be recovered by a conventional technique in the raflinate washer (DOS No. 1,941,704).

One embodiment of the process according to the invention is illustrated in FIG. 1 which, for simplicity, does not illustrate all the pumps, heat exchangers and intermediate containers, etc., which are required for practical operation.

A C -fraction I obtained by distillation from a crude cracked naphtha or from a cracked naphtha cut is thermally dimerized in conventional manner in a residencetime vessel 2 in which cyclopentadiene is preferably converted into dicyclopentadiene, Whilst the other diolefins such as isoprene and the piperylenes remain substantially unchanged. The hydrocarbon stream 3 which is rich in dicyclopentadiene but poor in cyclopentadiene is delivered to a liquid-liquid extractor 4 which, in the present case consists of a battery of mixing and settling chambers. A water-containing solvent stream 5 is introduced into the upper part of this extraction apparatus. The selective solvent flows in countercurrent to the starting material in the extraction column and preferentially dissolves the diolefins, such as isoprene, piperylenes, residual cyclopentadiene, and also cyclopentene, whilst leaving dicyclopentadiene together with the paraflins and the other monoolefins as rafiinate 6 which can be run off from the head of the extraction column. The diolefin-enriched solvent 7 which also contains all the more highly unsaturated C hydrocarbons present in the starting material, such as 1,2-butadiene, 1,3-butadiene and 2-butyne, and some of the butenes is run off at the lower end of the extractor 4 and delivered to the extract reflux column 8 in which by boiling the solution some of the dissolved hydrocarbons are run 01f overhead in gaseous form. The degree of boiling is governed by the required purity of the diolefin fraction to be produced.

The conjugated C -diolefins and cyclopentene which remain dissolved in the sump product 9 of the extract reflux column are delivered to the degasser 10 in which the solvent is freed from the remaining C -hydrocarbons by further boiling. The C -diolefin fraction which contains cyclopentene is run otf in the required purity as a head product 11 of the degasser and can be further separated by extraction, extractive distillation and/or distillation to recover the pure individual components. The sump prodnet of the degasser consists of substantially C -free regenerated water-containing solvent which is returned to the extractor after suitable cooling.

The head product 12 of the extract reflux column which contains all the C -hydrocarbons and some of the C -hydrocarbons from the extract solution, is delivered to another separation column 13 in which the C -hydrocarbons which have accumulated in the extract reflux are separated oif by distillation. The C -hydrocarbons consisting of 1,2-butadiene, 1,3-butadiene, 2-butyne and cis-/trans- Z-butene, are run off as lower-boiling head fraction 14 and thus removed from the system, whilst the C -free or C -poor sump product 15 is returned to the extractor as extract reflux after suitable cooling.

The raflinate 6 still containing a little solvent which is run off from the head end of the extractor is delivered to a raflinate washer 16 which, in the present case, can consist either of a mixer-settler battery or of a packed trickle column. The washing liquid 17, in the present case water, is delivered to the head of the washing column, the solvent-containing washing water 18 is run oif at the lower end and combined with the diolefin-containing solvent stream 7 or with the system as a whole at another suitable point. Solvent-free raflinate 19 is run 0E from the head of the washer section.

Cyclopentene and the C -diolefins, which are obtained according to the process of the invention are preferably used as the starting material for the manufacture of the individual pure components, such as, for example, isoprene, cyclopentene, cisand trans-1,3-pentadiene, which are used as monomers for the production of rubber-like polymers or for chemical synthesis, e.g. for the manufacture of plant protection agents. A further field of application of the C -diolefins, which are produced according to the invention is in the production of so-called petro resins and adhesive materials.

EXAMPLE 1 The C -fraetion from a crude cracked naphtha with the following contents of C -hydrocarbons and 1,4-pentadiene:

is delivered through pipe 1 in a quantity of 100 kgJhr. to a residence-time vessel 2 in which about 85% of the cyclopentadiene present in the starting material is thermally dimerized under pressure at 80 to 120 C. The C cut thus pretreated is cooled to a temperature of from 30 to 35 C. and delivered continuously through pipe 3 into the lower part of an extraction zone 4 which, in the present case, consists of a battery of 24 mixer-settler chambers arranged one above the other. 535 kg./hr. of a solvent, N-methylpyrrolidone (NMP) with a water content of by weight, are delivered into the uppermost mixing chamber of the extractor through the pipe 5. At the base of the extraction apparatus, extract solution containing 18% by weight of C and C -hydrocarbons is run off at a rate of 646 kg./hr. These hydrocarbons include all the 1,3-butadiene, 1,2-butadiene and Z-butyne present in the starting material, and most of the cis-/trans-butenes and 1,4-pentadiene. The remaining proportion of butenes and 1,4-pentadiene remains in the rafiinate phase which is run otf from the head of the extractor 6.

The extract solution flows through the pipe 7 into the extract reflux column 8 in which the liquid is heated until all the cis-ltrans-butene, 1,3-butadiene, 1,2-butadiene, 1,4- pentadiene, C -parafiins and C5'O1Cfil'lS and some of the 2-butyne and C -diolefins are removed at the head of the column. The purity of the diolefins remaining in the solvent is determined by the level of hydrocarbon removal.

The head product from the extract reflux column is run off through pipe 12 at a rate of 86 kg./hour and delivered to the so-called C -column 13. In this column containing 40 practical plates, head product is run oil in a quantity of 5 kg./hr. at a reflux ratio of R/E=22. In addition to C -hydrocarbons, it contains cis-/trans-butene, 24% by weight corresponding to 1.20

kg./hr.=80% of original quantity 1,3-butadiene, 8% by weight corresponding to 0.40 kg./

hr.=100% of original quantity 1,2-butadiene, 12% by weight corresponding to 0.60 kg./

hr.=100% of original quantity 2-butyne, 4% by weight corresponding to 0.20 kg./hr.=

50% of original quantity 1,4-pentadiene, 24% by weight corresponding to 1.20 kg./

hr.=86% of original quantity.

The sump product from the C -column, 81 kg./hr.,. is cooled to 30-35 C. and delivered as extract reflux through pipe 15 to the lowermost mixing chamber of the extraction apparatus.

Raflinate is removed from the uppermost separation chamber of the extractor in a quantity of 70 kgJhr/In addition to C -paraflins and olefins, it contains cis-ltrans-butene, 0.43% by weight corresponding to 0.30

kg./hr.=% of original quantity 1,4-pentadiene, 0.29% by weight corresponding to 0.20

kg./hr.=14% of original quantity.

The raflinate also contains 7.15% by weight of N- methylpyrrolidone corresponding to 5 kg./ hr. Accordingly, it is delivered through pipe 6 to a water wash 16 which, in the present case, also consists of an extraction apparatus and in which 6 mixer-settler chambers are arranged one above the other. The raffinate is introduced into the lowermost mixing chamber whilst the uppermost mixing chamher receives 5 kg./hr. of water through the pipe 17. The rafiinate is washed in countercurrent until free from NMP and then removed through pipe 19 in a quantity of 65 kg./ hr. The washing water containing 50% by weight of NMP is run ofi from the lowermost separation chamber through pipe 18 in a quantity of 10 lrgJ hour and combined with the input stream of the extract reflux column.

The sump product of the extract reflux column is run off through pipe 9 in a quantity of 570 kg./hr. and delivered to the degasser 10. In this column containing 30 practical plates, the extract solution is heated at a reflux ratio of RZE=1 until the solvent flows oil at the lower end substantially free from C It is cooled to a temperature of from 30-35 C. and recycled to the extractor. The C diolefin fraction is removed at the head of the column in a quantity of 30 kg./hr. 5 kg./hr. of water accumulate simultaneously with the hydrocarbons, being delivered to the raiiinate wash through pipe 17.

EXAMPLE 2 This example describes a comparison test carried out in accordance with the prior art, i.e. without separation of c -hydrocarbons in accordance with the invention.

C -cut of the same composition as in Example 1 is sub jected to a liquid-liquid extraction with Nwmethylpyrrolidone in the same way as described in Example 1. In a stable procedure according to Example 1, separation of the C -hydrocarbons in the so-called C -column .13 is eliminated by by-passing the product stream from pipe 12 to pipe 15 and the head product from the extract reflux column 8 delivered directly into the extractor 4 in accordance with the prior art (The Oil and Gas Journal; vol. 65 (1967), 2, p. 104). Thereafter the C -hydrocarbop content of the extract increases continuously. The dependence of the C -content upon time, based on the total content of hydrocarbons in the extract solution, is shown by the following table.

Stable operation of the extractor becomes increasingly more difficult as the C -content of the extract increases. A stable emulsion is formed so that extraction has to be stopped.

What is claimed is:

1. Process for separating conjugated C -dio1e fins and cyclopentene from a mixture of parafl'inic, olefinic and diolefinic Cg hydrocarbons containing unsaturated C -hydrocarbons which comprises:

(a) subjecting said mixture to liquid-liquid extraction;

(b) removing paraflins and mono-olefins as the raffinate of the liquid-liquid extraction;

(c) feeding the extract solution to an extract reflux column;

(d) subjecting the head product from the extract reflux column to distillation and removing C -hydrocarbons as ti e head fraction and returning the sump product to tigje liquid-liquid extraction step; and

(e) feeding the sump product form the extract reflux column to a degasser wherein C -diolefinic hydrocarbons and/or cyclopentene are removed as the head product and the sump product is returned to the liquid-liquid extraction step.

2. Process of claim 1 wherein said mixture contains cyclopentadiene which is dimerized prior to said liquidliquid extraction and is removed in step (b) with that raffinate.

3. Process of claim 1 wherein N-methyl pyrrolidone is used as the solvent for the liquid-liquid extraction.

7 8 4. Propess of claim 1 wherein a mixture of 'N-plethyl OTHER REFERENCES Pyrrplidone and go by weight water used The Oil and Gas Journal, Jan. 9, 1967, vol. 65, No. 2, a t he solvent for the hquld-llqmd extractlon. pp O1 and Refmms Cited 5 HERBERT LEVINE, Primary Examiner UNITED STATES PATENTS 3,674,883 7/1972 Schleppinghofi et al.

260681.5 R 203-46; 208326; 260-666 A, 681.5 R 3,707,575 12/1972 Muller et a1. 203-46 

